Radiation-curable poly(alpha-olefin) adhesives containing pendant olefinic functionality

Abstract: The invention relates to adhesive compositions comprising terpolymers of C₆-C₁₀ unsaturated α-olefin monomers, C₂-C₅ α-olefin monomers, and polyene monomers and an effective amount of photoactive crosslinking agent to crosslink composition upon exposure to a source of radiation.

Description: This invention relates to poly(α-olefin) compositions having enhanced radiation curability to provide adhesives having a superior balance of peel adhesion and cohesive strength at both ambient and elevated temperatures. A continuing need in the pressure-sensitive adhesive (PSA) art is the achievement of better control over various mechanical and process properties so that adhesives can be made specifically for highly demanding end use applications such as packaging, medical, and masking tapes. These applications require a proper balance of properties that changes with the particular end use. Among the earliest polymers to provide a reasonable balance of the properties required for satisfactory PSA performance were the natural and synthetic rubbers. However, these PSAs had poor aging properties, and the art quickly recognized the need to eliminate ethylenically unsaturated groups from the polymer backbone of rubber adhesives in order to improve their oxidative stability. The discovery of Ziegler-Natta (ZN) catalysts made possible polymerization of α-olefin monomers to high molecular weights. The homopolymers of the C 6 -C 10 α-olefins were naturally tacky and also had low toxicity, good aging and favorable environmental stability (i.e., low oxidation). These homopolymers were chemically inert, resistant to plasticizer migration, and relatively inexpensive. However, they had poor cohesive strength and therefore, lacked the shear adhesion necessary for high performance PSAs. Use of ZN catalysts to make homopolymers from α-olefin monomers and to make copolymers from mixtures of α-olefin and nonconjugated polyene monomers is known in the art and is succinctly summarized in Odian, G., "Principles of Polymerization", Ch. 8.4 (Second Edition J. Wiley & Sons, New York, 1981). For a more detailed discussion of the polymerization of α-olefins, see Boor, J., "Ziegler-Natta Catalysts and Polymerizations", Ch. 19 (Academic Press, NY, 1979). Adhesives derived primarily from C 6 or higher α-olefins are also known. U.S. Patent No. 3,542,717 describes poly(α-olefin) adhesive compositions comprising mixtures of polyolefin copolymers derived from olefin monomers with different molecular weights (i.e., copolymers from one α-olefin monomer having 11 to 20 carbon atoms and another having 4 to 20 carbon atoms.) U.S. Patent No. 3,635,755 describes polyolefin PSAs suitable for use as a single component PSA for surgical tapes that are substantially non-allergenic. Such adhesives can be made from homopolymers of the C 6 to C 11 α-olefins or from interpolymers of C 2 to C 16 α-olefins having an intrinsic viscosity of 1.5 to 7.0, a Williams plasticity of 0.8 to 4.0, and an acetone/heptane soluble fraction of less than 25% by weight. This patent does not teach radiation curing of these poly-olefin compounds. U.S. Patent Nos. 3,954,697 and 4,072,812 describe hot melt adhesives based respectively on propylene/C 6 -C 10 1-olefins wherein the C 6 -C 10 1-olefins comprise 40 to 60 mole percent of the composition and 1-butene/C 6 -C 10 1-olefins wherein the C 6 -C 10 1-olefins comprise 40 to 60 mole percent of the composition. These compositions have no detectable crystallinity by differential scanning calorimetry. These two patents also teach that copolymers containing only minor amounts of propylene or butylene (e.g. 5 to 20 wt%) are permanently tacky. Moreover, they teach that copolymers containing only minor amounts of propylene or butylene have little static shear and fail in the static shear test after less than 100 minutes. In addition, neither teaches the use of polyene monomers. U.S. Patent No. 4,178,272 describes hot melt adhesives based on a blend of poly(propylene-co-higher 1-olefin) containing 35 to 65 mole percent higher 1-olefins. A tackifying resin and crystalline polypropylene are added. Without the crystalline polypropylene homopolymer, the adhesive exhibits excessive creep under load. U.S. Patent No. 4,259,470 describes hot melt adhesives containing propylene, 1-butene or 1-pentene and 3 to 14 mole percent of at least one C 6 -C 10 linear α-olefin. Tackifying resins and plasticizing oils are added to the hot-melt compositions. U.S. Patent No. 4,288,358 describes hot-melt adhesive compositions containing terpolymers of 10 to 55 mole percent propylene, 15 to 60 mole percent 1-butene or 1-pentene, and 5 to 39 mole percent higher 1-olefins, i.e., C 6 -C 10 α-olefins. Tackifying resins and plasticizing oils are added to the hot-melt compositions. U.S. Patent No. 5,112,882 describes a radiation curable poly(α-olefin)-containing adhesive composition that is pressure sensitive at room temperature which upon cure yields an adhesive film having superior balance of peel and shear adhesion. The adhesive composition comprises (a) C 6 -C 10 α-olefin monomer(s) and 0 to 15 mole percent polyene monomers and (b) sufficient photoactive crosslinking agent to crosslink the composition upon irradiation. The radiation must be sufficient energy to generate free radicals so as to crosslink the composition. EP-A-0 003 194 relates to blends of plasticizing oils and compatible tackifiers with substantially amorphous or semicrystalline olefin copolymers containing a C 3 to C 5 linear α- olefin and 15 to 60 mole percent of a C 6 to C 10 linear α-olefin which are useful as hot-melt, pressure-sensitive adhesives. The present invention provides radiation curable poly(α-olefin) adhesive compositions with enhanced curability to adhesive films that have a superior balance of peel adhesion and cohesive strength at elevated temperatures comprising: a. an α-olefin polymer having the general formula wherein x, y, z' and z" are numbers designating the relative molar amounts of monomer units comprising the backbone chain of the polymer such that the polymer has a weight average molecular weight in the range of 50,000 to 5 million, x is from 45 to 98 mole percent of (x+y+z,+z''), y is from about 1 to 40 mole percent of the sum (x+y+z'+z''), and (z'+z'') is from 0.1 to 15 mole percent of (x+y+z'+z'') and either z' or z" can be zero; R 1 is an alkyl group having 4 to 8 carbon atoms, preferably 4 to 6 carbon atoms; R 2 is hydrogen or a group selected from linear and branched alkyl groups having 1 to 3 carbon atoms; R 3 is an unsaturated aliphatic hydrocarbyl group having 3 to 18 carbon atoms, the unsaturated group of which is separated from the of the α-olefin polymer backbone by at least one carbon atom, preferably selected from linear and branched alkenyl groups having 3 to 18 carbon atoms, non-conjugated polyethylenically-unsaturated aliphatic groups having 6 to 18 carbon atoms, cyclic alkenyl groups having 5 to 18 carbon atoms, and cyclic non-conjugated polyethylenically-unsaturated groups having 6 to 18 carbon atoms, or R 3 can also be -Q-R 7 , wherein R 7 is a C 2 to C 10 monovalent hydrocarbyl group containing one or more ethylenically unsaturated groups and Q is a divalent radical, -O-, or wherein R 8 and R 9 are the same or different C 1 to C 12 monovalent organic groups selected from alkyl, cycloalkyl, alkaryl, alkoxy, and aryloxy groups; and R 4 is hydrogen or R 4 together with R 3 and the carbon atoms to which they are attached forms an unsaturated or non-conjugated polyunsaturated monocyclic ring system having 6 to 18 carbon atoms, the unsaturated groups of which are separated from the of the α-olefin polymer backbone by at least one carbon atom; R 5 is hydrogen or a linear or branched alkyl group having 1 to 18 carbon atoms, or cyclic alkyl group having 5 to 18 carbon atoms; and R 6 is a linear or branched ethylenically- or non-conjugated polyethylenically-unsaturated aliphatic hydrocarbon group having 3 to 18 carbon atoms, a cyclic ethylenically or non-conjugated polyethylenically-unsaturated aliphatic hydrocarbyl group having 5 to 18 carbon atoms or a ethylmethacrylate group. and b. an effective amount of a photoactive crosslinking agent to crosslink the composition upon exposure to a source of actinic radiation. The present invention also provides a method of preparing the above radiation curable adhesive composition comprising the steps: a. providing the polymerization product of one or more C 6 -C 10 α-olefin monomers, one or more C 2 -C 5 α-olefin monomers and at least one non-conjugated polyene monomer selected from 1) a linear or branched polyene having 5 to 42 carbon atoms, 2) a monocyclic polyene having 6-20 or more carbon atoms, 3) a polycyclic polyene having 8 to 20 carbon atoms, 4) alkenyl aryl or arylene alkenyl substituted by mono- or polyethylenically unsaturated groups having 9 to 20 carbon atoms, or a combination of one or more of the foregoing, wherein said resultant polymer comprises 45 to 98 mole percent of C 6 -C 10 α-olefin repeat units, 1 to 40 mole percent C 2 -C 5 α-olefin repeat units, and 0.1 to 15 mole percent non-conjugated polyene repeat units; and then adding an effective amount of a photoactive crosslinking agent; and b. subjecting the admixture to sufficient actinic radiation to provide a cross-linked polymer. In another aspect, the present invention provides a method of preparing a radiation curable adhesive composition comprising the steps: a. polymerizing a C 6 -C 10 α-olefin monomer with at least one lower α-olefin monomer using a Ziegler-Natta catalyst to produce a saturated homopolymer or a copolymer, b. reacting the resulting α-olefin polymer with maleic anhydride in the presence of an initiator such as a peroxide and preferably an electron donor (e.g., triphenyl phosphite or triethyl phosphate) to produce a polyolefin adduct, c. reacting the maleated α-olefin polymer adduct with an ethylenically-unsaturated primary amine or isocyanate having 3 to 20 carbon atoms, and d. optionally, adding an effective amount of a photoactive cross-linking agent. Compositions with improved PSA properties may be obtained by blending two or more polymers of the invention or by blending one or more polymers with tackifying resins, preferably 1 to 150 parts by weight (pbw) of tackifying resin per 100 pbw polymer. The adhesives of the present invention can be applied to appropriate substrate surfaces by a wide range of processes, i.e., solution coating, solution spraying, hot-melt extrusion, emulsion coating, etc., to make adhesive tapes and adhesive transfer films. Unless otherwise indicated, the following definitions apply in this application: "C 6 -C 10 α-olefin monomer" means a linear or branched organic compound having 6 to 10 carbon atoms and one terminal ethylenically-unsaturated group and no other functional group; "polymer" means a homopolymer or a polymer, either random or blocked, derived from more than one monomer (e.g., copolymer, terpolymer, tetrapolymer, etc.); "polyene monomer" means a hydrocarbon of five or more carbon atoms containing two or more non-conjugated ethylenically unsaturated groups which may also contain 1 to 5 unitary heteroatoms selected from the group consisting of oxygen and silicon; "photoactive crosslinking agent" means a compound which, under the influence of suitable actinic radiation, initiates free radical formation and subsequent interchain crosslinking and which may or may not become incorporated therein, thus increasing the cohesive strength of the adhesive. The α-olefin polymers of the present invention have terminating groups, the identity of which depends upon the catalyst and components in the polymerizing composition. The terminating groups, because of their insignificant concentration, do not affect the essential properties of the polymers of the present invention. When R 1 contains from 4 to 8 carbon atoms, the ethylenically-unsaturated α-olefin polymers are tacky PSAs at room temperature (i.e., 20 to 25°C). Preferably, the ethylenically-unsaturated α-olefin polymer of the present invention has a glass transition temperature (T g ) not higher than about 0°C, more preferably not higher than about -10°C. Indeed, its T g can be as low as -70°C. PSA crosslinked α-olefin polymers of the present invention that have low T g 's tend to have superior adhesion. Furthermore, a crosslinked α-olefin polymer with a lower T g can be blended with larger amounts of tackifying resin to make coatings that exhibit less shocky peel adhesion. The ethylenically-unsaturated α-olefin polymers have inherent viscosities (IV) in the range of 0.5 to9 dl/g, preferably from 0.5 to 6 dl/g, at concentrations of 0.5 g/dl in toluene at 25°C, which values roughly correspond to average molecular weights of from 50,000 to 5,000,000, preferably 50,000 to 3,000,000, respectively. At an IV substantially below that preferred range, the ethylenically-unsaturated α-olefin polymer can be less likely to attain high internal or cohesive strength, especially at elevated temperatures. At viscosities substantially higher than 4 dl/g, the ethylenically-unsaturated α-olefin polymers preferably are coated from solution or hot melt extrusion. The ethylenically-unsaturated α-olefin polymer can be produced by the following methods. In a first method, a C 6 -C 10 α-olefin monomer is polymerized with a C 2 -C 5 α-olefin monomer and a non-conjugated polyene selected from 1) a linear or branched polyene having 5 to 42 carbon atoms, 2) a monocyclic polyene having 6 to 20 or more carbon atoms, 3) a polycyclic polyene having 8 to 20 carbon atoms, and/or 4) alkenyl aryl or arylene alkenyl substituted by mono- or polyethylenically unsaturated groups having 9 to 20 carbon atoms, using a Z-N catalyst to produce a terpolymer containing ethylenic unsaturation. In the terpolymer produced by this first method, M 3 in formula II, has, for example, structures such as III, IV and V (below) when the diene is linear, and structures such as VI, VII, and VIII (below) when the diene is cyclic, wherein s is an integer from 1 to 14, preferably 2 to 4, and t is an integer from 1 to 14, preferably 2 to 4. A second method involves the steps of: a. polymerizing a C 6 to C 10 α-olefin monomer with at least one lower α-olefin monomer using a Z-N catalyst to produce a saturated homopolymer or a copolymer, b. reacting the resulting α-olefin polymer with maleic anhydride in the presence of an initiator such as a peroxide and preferably an electron donor (e.g., triphenyl phosphite or triethyl phosphate) to produce a maleated α-olefin polymer adduct, c. reacting the maleated α-olefin polymer adduct with an ethylenically-unsaturated primary amine or isocyanate having 3 to 20 carbon atoms, either in solution or in a melt, (e.g., in an extruder) to produce an ethylenically-unsaturated α-olefin polymer, and d. optionally, adding an effective amount of a photoactive crosslinking agent. In the resulting α-olefin polymer, M 3 of Formula II has structures such as IX and X. Alpha-olefin monomers that can be used in the preparation of the ethylenically-unsaturated α-olefin polymers of the present invention can have from 2 to 10 carbon atoms. Representative examples include, but are not limited to, ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene. Non-conjugated dienes that can be used in the preparation of the α-olefin polymers of the present invention have 5 to 42 carbon atoms. Representative examples include, but are not limited to, 1,4-pentadiene, 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, and 1,13-tetradecadiene; cyclic dienes such as 1,4-cyclohexadiene, bicyclo[2.2.1]hept-2,5-diene, bicyclo[2.2.2]oct-2,5-diene, bicyclo[2.2.2]oct-2,6-diene, 1,7,7-trimethylbicyclo[2.2.1]hept-2,5-diene, 5-allylbicyclo[2.2.1]hept-2-ene, and 1,5-cyclooctadiene; and aromatic dienes such as bis(ω-alkenyl)benzenes such as 1,4-diallylbenzene, and 4-allyl-1H-indene. Other suitable polyene monomers useful in the practice of the present invention are comprised of hydrocarbons containing two to four ethylenically unsaturated groups. 5-ethylidene-2-norbornene, dicyclopentadiene, limonene, beta-pinene, methylene-norbornene and various alkenyl-norbornenes with the structure: where m is an integer from 1 to 18. Other suitable polyene monomers useful in the practice of the present invention are diallyl ether, di(3-butenyl) ether, 4-(2-propenyl)-1-benzene, diallylbenzene, 3-butenylethenyldimethylsilane, dimethyldi(2-propenyl)silane, tetra(3-butenyl)silane, tetravinylsilane, diethenyldimethylsilane, di(3-butenyl) dimethylsilane, di(3-butenyl)-dimethoxysilane and diethenyldiethoxysilane. The α-olefin polymers of the present invention can be either random co-, ter-, tetra-polymers; or blocks of homopoly(α-olefins) interspersed with polyene units, depending upon the relative reactivities of the various monomers. When the reactivity at each end of the alpha, omega dienes are about equal, gel-permeation chromatographic analysis (with low-angle light scattering detector) of polymers containing these monomers show more branching than observed with monomers having double bonds of unequal reactivity. When diene monomers in which the reactivities of the double bonds are unequal are polymerized, as is the case with 7-octenyldimethylvinylsilane, essentially linear polymers are formed during ZN polymerization. The α-olefin and polyene monomers can be polymerized in the presence of Ziegler-Natta catalysts over a wide range of temperatures, e.g., 0 to 140°C, preferably 30 to 90°C. The polymerization can be done in bulk or in inert solvents. Suitable examples of inert solvents include, but are not limited to, the aliphatic, aromatic, and cycloaliphatic hydrocarbon solvents, i.e., pentane, hexane, heptane, benzene, toluene, cyclopentane, and cyclohexane. The amount of catalyst used is preferably in the range of 0.1 g to 5 g per kg of monomer, more preferably 0.2 to 3 g per kg of monomer, and most preferably, 0.5 to 2 g per kg of monomer. ZN catalysts are well known in the art and are disclosed, for example, in Odian, G., supra. and Boor, J., supra. Suitable photoactive crosslinking agents for use in the compositions of the invention, which are free of elemental sulfur include, but are not limited to: aldehydes, such as benzaldehyde, acetaldehyde, and their substituted derivatives; ketones such as acetophenone, benzophenone and their substituted derivatives; quinones such as the benzoquinones, anthraquinone and their substituted derivatives; thioxanthones such as 2-isopropylthioxanthone and 2-dodecylthioxanthone; and certain chromophore-substituted vinyl halomethyl-sym-triazines such as 2,4-bis-(trichloromethyl)-6-(3',4'-dimethoxyphenyl)-symtriazine. The concentration of photoactive crosslinking agent is in the range of 0.05 to 6.0% (by wt.), preferably 0.1 to 2% (by wt.), and more preferably 0.5 to 1.5% (by wt.). The adhesive composition of the present invention can be coated from solution by any of the coating processes known in the art, such as knife coating, roll coating, gravure coating, curtain coating, etc. Useful coating thicknesses for the present invention are in the range of 0.5 to 15 mg/cm 2 , preferably from 2.0 to 7.0 mg/cm 2 . Furthermore, some of the compositions of the invention can be applied by extrusion coating with no solvent present, thereby eliminating environmental and toxicity problems associated with solution coating processes. In addition, the adhesive composition can be cured using a source of actinic radiation of sufficient energy (i.e., wavelength range) to generate free radicals when incident upon the particular photoactive crosslinking agent selected for use in the composition. The preferred wavelength range for the photoactive crosslinking agents disclosed above is 400 to 250 nm. The radiant energy in this preferred range of wavelengths required to crosslink the adhesive film of the invention is 100 to 1500 mJ/cm 2 , more preferably 200 to 800 mJ/cm 2 . Additional details of the photocure process are disclosed in U.S. Patent Nos. 4,181,752 and 4,329,384. The adhesive compositions of the present invention, with or without a photoactive crosslinking agent, may be cured by electron beam irradiation. The crosslinked adhesive films preferably have a gel content in the range of from 2 to 95% (by wt.) percent, more preferably from 30 to 80% (by wt.), and most preferably from 50 to 70% (by wt.) when the gel content has been corrected for soluble tackifying resins and other additives as hereinafter described. Adding one or more tackifying resins to the inventive composition can provide a PSA having improved tack, lower viscosity, improved coatability, good heat stability, and improved peel adhesion. The shear adhesion of the tackified compositions can be enhanced by radiation cure with no loss of peel adhesion. The resulting adhesives have the high internal or cohesive strength required for box sealing tape or masking tape applications. Compatible tackifying resins useful in the radiation curable adhesive compositions of the invention include resins derived by polymerization of C 5 -C 9 unsaturated hydrocarbon monomers, polyterpenes, synthetic polyterpenes, and the like. Hydrocarbon tackifying resins can be prepared by polymerization of monomers consisting primarily of olefins and diolefins and include, for example, residual byproduct monomers of the isoprene manufacturing process. These hydrocarbon tackifying resins typically exhibit Ball and Ring Softening Points (ASTM D465-59) of from about 80°C to 145°C; acid numbers of from about 0 to 2, and saponification values of less than one. Examples of such commercially available resins based on a C 5 -C 9 olefin fraction of this type are Wingtack™ 95, Wingtack™ 115 and Wingtack™ Plus tackifying resins (Goodyear Tire and Rubber Co.; Akron, OH); Regalrez™ 1078 and Regalrez™ 1126 resins (Hercules Chemical Co. Inc., Wilmington, DE); Arkon resins, such as Arkon™ P115 (Arakawa Forest Chemical Industries; Chicago IL); and Escorez™ resins (Exxon Chemical Co.; Newark, NJ). Other suitable resins include the terpene polymers, such as polymeric resinous materials obtained by polymerization and/or copolymerization of terpene hydrocarbons such as their mixtures, including carene, isomerized pinene, terpinene, terpentene, and various other terpenes. Commerically available resins of the terpene type include the Zonarez™ B and 7000 terpene 5 series (Arizona Chemical Corp., Wayne, NJ). Typical properties reported for the Zonarez™ terpene resins include Ball and Ring Softening of less than one, and Saponification Numbers (ASTM D464-59) of less than one. The terpene resin used in examples below is a poly(beta-pinene) resin, Piccolyte™ A115 (Hercules Chemical Co. Inc.), which has a Ball and Ring Softening Point of 115°C, an Acid Number 4 of one, and Iodine Number 4 of 190. The tackifying resins may contain ethylenic unsaturation; however, saturated tackifying resins are preferred for those applications where oxidation resistance is important. The total amount of tackifying resins in the composition ranges up to about 150 pbw, more preferably 5 to 50 pbw, and most preferably 25 to 35 pbw, per 100 pbw of polymer. Saturated tackifying resins such as Regalrez™ 1078 and Arkon™ P115 are preferred because they yield a higher gel content upon equivalent treatment by an activated crosslinking agent. Minor amounts of additives can also be included in the composition to provide adhesives for special end uses. Such additives may include pigments, dyes, plasticizers, fillers, stabilizers, ultraviolet absorbers, antioxidants, processing oils, and the like. The weight percentages of these additives can vary from 0.1 to 50% depending on the end use desired. The adhesive composition of the present invention can be coated onto a wide range of substrate materials such as polymer films (e.g., polyethylene terephthalate (PET) and biaxially oriented polypropylene (BOPP)); woven and non-woven fabrics; metals and metal foils such as aluminum, copper, lead, gold and the like; paper; glass; ceramics; and composite materials comprised of laminates of one or more of these materials. The present invention provides α-olefin polymers containing adhesive compositions that are radiation-curable to yield adhesive films with an improved balance of peel adhesion and cohesive strength, especially at elevated temperatures. The peel adhesion and cohesive strength values are capable of being varied independently to achieve desired values. Adhesive films of the invention preferably have peel values in the range of 2 to 100 N/dm and shear values in the range of 1 to 10,000 or more minutes. The present invention provides PSA that have good cohesive strength at elevated temperatures. The PSA tapes of the invention are ideally suited for automotive masking tape applications as well as other tape applications which require good cohesive strength at elevated temperatures and yet be readily removed from painted or other surfaces leaving essentially no adhesive residue. Another embodiment of the invention comprises a laminated structure of at least a first and a second substrate, the substrates being joined by a layer of the adhesive composition of the invention. At least one of the substrates is capable of transmitting actinic or electron beam radiation so that the adhesive film may be cured. In some applications primers may be useful for improving the adhesion of the adhesive to some substrates. Useful primers for the practice of the present invention include a triblock copolymer of styrene-ethylene/butylene-styrene grafted with maleic anhydride, both alone and in combination with amorphous polypropylene (such as are described in U.S. Patent Nos. 4,386,135, 3,957,724, and 2,532,011). These form a special class of substrates on which the composition of the invention can be coated and subsequently radiation cured to form adhesive transfer films. TEST METHODS: The test procedures used in the examples to evaluate and compare the properties of the PSA compositions and tapes made from them are industry standard tests. These tests are described in detail in various publications of the American Society for Testing Materials (ASTM) (Philadelphia, PA) and the Pressure Sensitive Tape Council (PSTC) (Glenview, IL). References to these standards are also given. Shear Strength (ASTM D-3654-78; PSTC-7) Shear strength is a measure of the cohesiveness or internal strength of an adhesive. It is based upon the amount of force required to pull an adhesive strip from a standard flat surface in a direction parallel to the surface to which it has been affixed with a definite pressure. It is measured in units of time(minutes) required to pull a standard area of PSA coated sheet material from a stainless steel test panel under stress of a constant, standard load. The tests were conducted on adhesive coated strips applied to a stainless steel panel such that a 12.7 mm by 12.7 mm portion of each strip was in firm contact with the panel with one end portion of the tape being free. The panel with coated strip attached was held in a rack such that the coated surface of the panel forms an angle of 182° with the vertical tape free end which is then tensioned by application of a force of one kilogram applied as a hanging weight from the free end of the coated strip. The 182° angle is used to negate peel forces thus insuring that only the shear forces are measured, thereby more accurately determining the holding power of the tape being tested. The time elapsed for each test specimen to separate from the steel panel is recorded as the shear strength. Mode of Failure (MOF) The time at which the mass falls is called "Shear Test" and is reported as "5000 + " if the tape has not failed after 5000 minutes. With each Shear is indicated the mode of failure as follows: po = pop-off, i.e., 75-100% adhesive failure from steelplate: f = cohesive failure (both surfaces completely covered by adhesive); The pop-off failure mode is preferred because it is indicative of adhesive failure of the adhesive/steel interfacial bond as opposed to cohesive failure of the adhesive. Adhesives of various shear adhesions, all within the range of the present invention (1 to 10,000 minutes), are preferred depending on end-use applications. Two specimens of each tape were tested and the shear tests were averaged to obtain the shear value. Peel Adhesion [ASTM D 3330-78; PSTC-1(11/75)] Peel adhesion is the force required to remove a PSA coated test specimen from a test panel measured at a specific angle and rate of removal. In the examples, this force is expressed in Newtons per decimeter (N/dm) width of coated sheet. The procedure followed is: (1) A 25.4 mm x 150 mm test specimen was applied to a horizontally positioned clean glass test plate such that 12.7 mm of the specimen extended beyond the plate. A 2.3 kg rubber roller was rolled over the test specimen twice to insure good contact between the specimen and the test plate. (2) The free end of the specimen is doubled back nearly touching itself so the angle of removal is 180°. The free end is attached to the adhesion tester scale. (3) The glass test plate is clamped in the jaws of tensile testing machine which is capable of moving the plate away from the scale at a constant rate of 2.3 meters per minute. (4) The scale reading in Newtons is noted as the tape is peeled from the glass surface, and the average, peak, and valley reading from the entire length of peeled tape specimen are recorded. Inherent Viscosity [ASTM D 2857-70 (Reapproved 1977)] In order to understand the benefits derived from the teaching of this invention, it is necessary to relate the improvements in shear strength and processability to the molecular weight of the PSA. The inherent viscosity of 10 ml sample of a 0.5 g/dl solution of the sample in toluene is measured using a Cannon-Fenske #50 viscometer in a water bath controlled at 25°C. The solvent used is specified in the examples. Percent Gel Test [ASTM D 3616-82] The percent gel is used as an indication of cure level. The tapes containing tackifying resins are corrected to the actual percent gel. The corrected percent gel is 100 times the gelled mass divided by the total mass of material that is capable of forming a gelled network. Soluble materials such as tackifiers are subtracted out when determining the gel fraction. Crosslinking by radiation improves the creep and shear resistance of pressure-sensitive adhesives. Many important properties of crosslinked PSAs vary with the gel content. Hence, determination of the gel content provides a means for controlling the process and thereby raising the quality of the tape. Extraction tests permit verification of the proper gel content of polyolefin PSAs and they also permit comparison between different crosslinked adhesives and their specific end uses. Gel Content Determination A square test specimen (3.81 cm x 3.81 cm) containing approximately 0.06 g of PSA is cut from the tape and placed in a 120-mesh stainless steel basket measuring approximately 4.4 x 4.4. x 1.3 cm. The contents are weighed to the nearest 0.1 mg and then immersed in a capped beaker containing sufficient toluene to cover the specimen. After extraction for 24 to 48 hours, the basket (containing the specimen) is removed, drained, and placed in an oven at 93°C. The basket and specimen are dried to a constant weight and the gel content is determined as follows: Extract % = weight lost during extraction x 100 weight of original specimen Gel content = 100 - percent extract The gel content of the adhesive was determined after correcting for the tackifier. (and backing for a tape construction). Two specimens of each tape were tested and the results were averaged to obtain the gel content value. Percent Residue Test An aluminum panel painted with an automotive basecoat/clearcoat (BC/CC) acrylic enamel paint system or the automotive 50J™ acrylic enamel paint (Ford Motor Co.; Detroit, Mi) is used as a test panel for the percent residue test. Tapes are applied at room temperature to the test surface followed by rolling the test specimen with two passes of a 2 Kg rubber-coated metal roller. After one hour in an air-circulating oven at either 121°C or 150°C, the tape is peeled back, while hot, at an angle of 135° at an approximate rate of 1.9 m/min across half of the panel. Thereafter, the test panel is allowed to cool to room temperature and the tape samples are peeled from the remainder of the test panel at an angle of 45° peel and a rate of approximately 1.9 m/min. The panel is then visually examined for any adhesive residue. This invention is further illustrated by the following examples of preferred embodiments thereof. Unsaturated α-olefin copolymers 1-Hexene/propylene/4-vinylcyclohex-1-ene copolymer (U-1) A reaction vessel equipped with a mechanical stirrer, reflux condenser and temperature controller was dried and filled with nitrogen. The vessel was charged with 300 ml 1-hexene, 300 ml toluene, 7.5 ml 4-vinylcyclohex-1-ene, and 1.1 ml diethyl aluminum chloride. The reactor was heated to 60°C, 0.21 g Aluminum Activated Reduced titanium trichloride, AATiCl 3 (Stauffer Chemical Co.; Hartford, CT) was introduced, and propylene was bubbled into the reaction mixture at a rate of about 60 cm 3 /min for about 2 hours. Methanol was added to the reaction mixture to terminate the polymerization. The reactor was cooled to room temperature, excess methanol was added to precipitate the polymer, and the precipitated polymer was washed twice with methanol. Reaction product of maleated polyolefin (MPO) and isocyanatoethyl methacrylate (U-2) 52.0 g of 1.2 mole percent maleated hexene/propylene (60/40) copolymer having a melt viscosity of 7680 cp at 190°C (available from Eastman Chemical Co. as TX-P1824-013) was dried in a vacuum at 70°C for about 16 hours and dissolved in 250 ml toluene. The solution was refluxed under nitrogen, and about 50 ml toluene was distilled out to ensure recyclization of diacid grafts and to remove residual water in the polymer. To this was added 0.63 g isocyanatoethyl methacrylate (IEM), and the reaction mixture was gently refluxed for about 3 hours. IR analysis showed that all isocyanate groups were consumed indicating completion of the reaction. The copolymer was concentrated to a viscosity suitable for coating on PET backing (approximately 25 to 30% solids). Reaction product of MPO and isocyanatoethyl methacrylate (U3) 53 g of 2.6 mole percent maleated hexene/propylene (60/40) copolymer having a melt viscosity of 9840 cp at 190°C (available from Eastman Chemical Co. as TX-1768-85) was dissolved in 250 ml toluene. The solution was refluxed under nitrogen, and about 50 ml toluene was distilled off to ensure recyclization of the acid grafts and to remove residual water in the polymer. To this was added 2.03 g of isocyanatoethyl methacrylate (IEM), and the reaction mixture gently refluxed for about 3 hours. Progress of the reaction was monitored as described above. The copolymer was concentrated to a viscosity suitable for coating on PET backing (approximately 25 to 30 percent solids). Reaction product of MPO and 4-aminostyrene (U4) 17 g of 4.4 mole percent maleated hexene/propylene (60/40) copolymer having melt viscosity 4700 cp at 190°C (available from Eastman Chemical Co. as TX P1824-011) was dissolved in 150 ml toluene. The polymer solution was refluxed under nitrogen and about 20 ml toluene was distilled out to ensure recyclization of the acid grafts and to remove residual water from the polymer. To this was added 1.24 g of 4-aminostyrene (PAS), and the mixture was gently refluxed for about 3 hours. Progress of the reaction was monitored as described above. The copolymer was concentrated to a viscosity suitable for coating on PET backing (approximately 25 to 30% solids). Reaction product of MPO and 4-aminostyrene (U5) 15 g of 4.4 mole percent maleated hexene/propylene (60/40) copolymer as described in the preparation of U4 was dissolved in 150 ml toluene. The solution was refluxed under nitrogen to ensure recyclization of the 5 acid grafts and about 20 ml toluene was distilled out to remove residual water in the polymer. To this was added 0.53 g of PAS, and the reaction mixture gently refluxed for about 3 hours. Progress of the reaction was monitored as described above. The copolymer was concentrated to a viscosity suitable for coating on PET backing (approximately 25 to 30% solids). Reaction product of MPO and 4-aminostyrene (U6) 16.7 g of 4.4 mole percent maleated hexene/propylene (60/40) copolymer as described in the preparation of U4 was dissolved in 150 ml toluene. The solution was refluxed under nitrogen, and about 20 ml toluene was distilled out to ensure recyclization of the acid grafts and to remove residual water in the polymer. To this mixture was added 0.30 g of PAS, and the reaction mixture was gently refluxed for about 3 hours. Progress of the reaction was monitored as described above. The copolymer was concentrated to a viscosity suitable for coating on PET backing (approximately 25 to 30% solids). Reaction product of MPO and allylamine (U7) 27.1 g of 4.4 mole percent maleated hexene/propylene (60/40) copolymer as described in the preparation of U4 was dissolved in 150 ml toluene. The solution was refluxed under nitrogen to recyclize the acid grafts, and about 20 ml toluene was distilled out to remove residual water in the polymer. To this was added 0.94 g of allyl amine, and the reaction mixture gently refluxed for about 3 hours. Progress of the reaction was monitored as described above. At the end of the reaction, the copolymer was concentrated to a viscosity suitable for coating on PET backing (approximately 25 to 30% solids). Examples 1-19 Pressure Sensitive Adhesives From Unsaturated Polyolefins Blends of 100 parts of unsaturated α-olefin copolymers U-1, U-2, U-3, U-4, U-5, U-6, and U-7, with and without 33 phr (parts per 100 parts) by weight tackifier resin, 1.0 phr of photoinitiator, and 0.25 phr Irganox™ 1010 antioxidant in toluene were knife coated to yield a dry adhesive coating thickness of 38 µm on a 57 µm thick biaxially oriented poly(ethylene terephthalate)(PET) film. Each coating was dried for 5 minutes at 70°C and exposed to doses of 300 to 1200 mJ/cm 2 from medium pressure mercury lamps. The compositions prepared and the test results obtained for each are recorded in Table I. Comparative Examples C1, C2, C3, C4, C5, C6 and C7 Control PSA construction consisted of untackified and uncured samples of the unsaturated α-olefin polymers (U-1, U-2, U-3, U-4, U-5, U-6, and U-7, as previously described) which were solution coated onto a 57 µm biaxially oriented PET film to produce dry PSA films having a nominal thickness of 38 µm. The coating conditions and subsequent test protocol was the same as described for Examples 1-19. The data in Table I reveals that unsaturated polyolefin PSA compositions containing propylene as the C 2 -C 5 α-olefin monomer, when irradiated with ultraviolet light, leave less than 5% residue in the Percent Residue test and, particularly, that where the unsaturation is introduced into propylene-containing polyolefin by maleation followed by reaction with an amino or isocyanate group substituted unsaturated compound, excellent shear values at 25°C are obtained and less than 5% adhesive residue (in most cases no adhesive residue) is left in the Percent Residue Test. The samples of the comparative examples leave 25 to 100% adhesive residue.

Claims: A composition radiation curable to an adhesive comprising: a. an α-olefin polymer having the general formula wherein x, y, z' and z" are numbers designating the relative molar amounts of monomer units comprising the backbone chain of the polymer such that the polymer has a weight average molecular weight in the range of 50,000 to 5,000,000, x is from 45 to 98 mole percent of (x+y+z'+z"), y is from 1 to 40 mole percent of (x+y+z'+z"), and (z'+z") is from 0.1 to 15 mole percent of (x+y+z'+z") and either of z' or z" can be zero; R 1 is an alkyl group having 4 to 8 carbon atoms; R 2 is hydrogen or a group, selected from linear and branched alkyl groups having 1 to 3 carbon atoms; R 3 is an unsaturated aliphatic hydrocarbyl group having 3 to 18 carbon atoms, the unsaturated group of which is separated from the of the α-olefin polymer backbone by at least one carbon atom, preferably selected from linear and branched alkenyl groups having 3 to 18 carbon atoms, non-conjugated polyethylenically-unsaturated aliphatic groups having 6 to 18 carbon atoms, cyclic alkenyl groups having 5 to 18 carbon atoms, and cyclic non-conjugated polyethylenically-unsaturated groups having 6 to 18 carbon atoms, or R 3 can also be -Q-R 7 , wherein R 7 is a C 2 to C 10 monovalent hydrocarbyl group containing one or more ethylenically unsaturated groups and Q is a divalent radical, -O-, or wherein R 8 and R 9 are the same or different C 1 to C 12 monovalent organic groups selected from alkyl, cycloalkyl, alkaryl, alkoxy, and aryloxy groups; and R 4 is hydrogen or R 4 together with R 3 and the carbon atoms to which they are attached forms an unsaturated or non-conjugated polyunsaturated monocyclic ring system having 6 to 18 carbon atoms, the unsaturated groups of which are separated from the of the α-olefin polymer backbone by at least one carbon atom; R 5 is hydrogen or a linear or branched alkyl group having 1 to 18 carbon atoms or cyclic alkyl group having 5 to 18 carbon atoms; and R 6 is a linear or branched ethylenically- or non-conjugated polyethylenically-unsaturated aliphatic hydrocarbon group having 3 to 18 carbon atoms, a cyclic ethylenically or non-conjugated polyethylenically-unsaturated aliphatic hydrocarbyl group having 5 to 18 carbon atoms; or a ethylmethacrylate group; and b. an effective amount of a photoactive crosslinking agent to crosslink the composition upon exposure to a source of actinic radiation. The adhesive composition of claim 1 wherein said photoactive crosslinking agent is selected from the group consisting of aldehydes, ketones, quinones, thioxanthones and s-triazines. The adhesive composition of claims 1 to 2 further comprising a tackifying resin. The adhesive composition of claim 3 wherein said tackifying resin is a hydrocarbon resin. The adhesive composition of any of claims 3 to 4 wherein said tackifying resin is present in an amount up to 150 parts by weight per 100 parts by weight of said α-olefin polymer. The adhesive composition of claim 1 wherein R 1 is an alkyl group comprising 4 to 6 carbon atoms. The adhesive composition of claims 1 to 6 wherein said composition has been crosslinked. An article comprising the adhesive composition of claims 1 to 7 coated on a substrate. A method of preparing the radiation cured adhesive composition of claim 7 comprising the steps: a. providing the polymerization product of one or more C 6 -C 10 α-olefin monomers, one or more C 2 -C 5 α-olefin monomers, and at least one non-conjugated polyene monomer selected from 1) a linear or branched polyene having 5 to 42 carbon atoms, 2) a monocyclic polyene having 6-20 or more carbon atoms, 3) a polycyclic polyene having 8 to 20 carbon atoms, 4) alkenyl aryl or arylene alkenyl substituted by mono- or polyethylenically unsaturated groups having 9 to 20 carbon atoms, or a combination of one or more of the foregoing, wherein said resultant polymer comprises 45 to 98 mole percent of C 6 -C 10 α-olefin repeat units, 1 to 40 mole percent C 2 -C 5 α-olefin repeat units, and 0.1 to 15 mole percent non-conjugated polyene repeat units, and then adding an effective amount of a photoactive crosslinking agent; and b. subjecting the admixture to sufficient actinic radiation to provide a cross-linked polymer. A method of preparing a radiation curable adhesive composition comprising the steps of: a. polymerizing a C 6 -C 10 α-olefin monomer with at least one C 2 -C 5 α-olefin monomer using a Ziegler-Natta catalyst to produce a saturated homopolymer or a copolymer, b. reacting the resulting α-olefin polymer with maleic anhydride in the presence of an initiator such as a peroxide and preferably an electron donor (e.g., triphenyl phosphite or triethyl phosphate) to produce a polyolefin adduct, c. reacting the maleated α-olefin polymer adduct with an ethylenically-unsaturated primary amine or isocyanate having 3 to 20 carbon atoms, and d. optionally, adding an effective amount of a photoactive cross-linking agent.

Inventors: BABU GADDAM N, PETERSON JAMES R, BABU, GADDAM N., PETERSON, JAMES R., BABU, GADDAM N., C/O MINNESOTA MINING AND, PETERSON, JAMES R., C/O MINNESOTA MINING AND
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1994
Main classification: C09J123
IPC codes: C08F290, C09J4, C08F299, C09J123, C08F2, C08F8